Venetian blinds consist of at least two ladders, either ladder cords or ladder tapes, each having laterally spaced side members and cross rungs defining openings to receive slats. The assembly can be done manually or by machine and in the latter case the ladders by ladder feed means are intermittently fed lengthwise of the side members and by ladder guide or -spreader means are guided so that two adjacent rungs of each ladder are held apart at least substantially parallel to one another and the portions of the longitudinal side members at the location of the two adjacent rungs are held apart at least substantially parallel to one another, thereby to give a predetermined shape to the associated opening. The slat material is fed by slat material feed means along a defined path through the relevant associated openings, thereby guided by slat material guiding means.
This works reasonably satisfactorily for slats having a width of 25 mm or more, but it has been found that it is difficult to achieve satisfactory results with narrower blinds, for example blinds having slats which are 16 mm wide. These slats themselves tend to be rather flimsy and the opening in the ladders into which they are to be introduced is relatively small. Furthermore, in order to cover a given window surface a much greater number of slats need to be inserted into the ladder. It will be appreciated that the speed of the assembly machines is limited by the operation of the assembly work stations and the increase of speed which would be necessary to manufacture a blind to cover a given window space using these much narrower slats is not enhanced by the use of smaller dimensions of the slats and the openings formed in the ladders.